Recycling of materials is often practiced to conserve raw materials. Contaminated materials are often treated to decontaminate their main constituents to allow reuse of these constituents. In general, isolated contaminants or contaminated articles not readily susceptible to decontamination are intended, in accordance with past practice, to be disposed of in ways that put the emphasis on destruction or isolation rather than on considerations of reuse. What therefore has happened and is continuing to happen is that increasing quantities of clean materials are turned into contaminated materials that then have to be disposed of in safe ways.
A wide variety of articles and their uses are discussed herein, one type of which is a container to confine waste.
Before the use of modern storage modules, in many instances nuclear waste and hazardous waste were stored in 55-gallon steel drums. In the case of very low level radioactive waste, such drums are still used, many times being overpacked in plastic containers such as polyethylene, polypropylene and the like. More sophisticated, all steel containment systems, having thick steel walls and an adjustable shielding core, are described in U.S. Pat. No. 4,451,739 (Christ et al.). There, exterior or interior lead or steel wire which serves to attenuate of gamma rays, can be wrapped in as many layers as appropriate to the contaminant waste material's radioactivity.
More recently, outer waste container systems have been made with uncontaminated concrete reinforced with large, uncontaminated metal bars, called "rebar" construction, or a steel reinforcing mesh basket, to improve the strength of the container. However, use of large metal bars and steel mesh generally require thick walled containers. Examples of such containers are shown in U.S. Pat. Nos. 4,950,426 (Markowitz et al.) and 4,845,372 (Mallory et al.). In these containers, filler is used to seal the void space between the outer container and, for example, compacted steel-walled storage drums which alone, contain the radioactive material or hazardous material.
in some instances, various types of fibers are used in place of bars or mesh to reinforce concrete in waste containment vessels. In U.S. Pat. No. 4,995,019 (Cataloyoud et al.), a tight-sealing, drum-covered containment vessel is taught, where cast iron or stainless steel fibers are distributed in a random manner in the concrete container. U.S. Pat. No. 4,167,491 (Gablin et al.) describes disadvantages associated with concrete, the most serious of which is the potential of some radioactive material leaching therefrom. There, water which contains radioactive nickel and cobalt-60 is passed through cation resin exchange beads to concentrate the contaminants, then the wet beads are mixed with an aqueous dispersion of a hydrophilic urea-formaldehyde plastic resin obtaining an acidic curing agent, to form a solid waste block for disposal in a steel or cast iron outer container.
In U.S. Pat. No. 4,594,513 (Suzuki et al.), steel or carbon fibers, or metal gauze, are used to reinforce concrete containers, which containers are then impregnated with a polymerizable monomer, to provide a water impermeable lining. Other ingredients that can be added to concrete multipurpose contaminated waste containers having polymeric liners include amorphous metal fibers, fly ash, and silica fume, as taught in U.S. Pat. No. 5,225,114 (Anderson et al.). There, the container needs no exterior concrete overpack barrier and is also transportable and storable. In other instances, hazardous waste is high-density packed within a solidified radiation shielding by centrifugally casting waste material and polyorganic compounds or cementitious material, to form a monolith having high strength and structural integrity, such as taught in U.S. Pat. No. 5,075,045 (Manchak, Jr.). Radioactive wastes can also be classified, segregated, and cast with a shielding material which encapsulates it and prevents the escape of radiation, as taught in U.S. Pat. No. 4,897,221 (Manchak, Jr.)
In Atomkernenergie-Kerntechnick, Bd. 41 (1982), No. 4, pp. 279 to 280, "Proposal for the Disposal of Contaminated Steel Parts from Shut Down Nuclear Power Plants", by W. M. Francioni, shielding materials and disposal of highly radioactive material are discussed. This article describes disposal of waste material by using it to form containers for other waste. It discloses, for example, that, theoretically, any suitable material, such as concrete, iron, or lead can be used for the container. It describes in detail a thick concrete transport container, with an additional, separate, inner shielding liner made of melted, cast, solidified, radioactive steel from reactor tubes, and the like. This article also discusses questions regarding Secondary wastes during melting the radioactive steel, and, whether the use of such metal shields would be economical since the metal used, at that time, would have had to be decontaminated to a maximum surface activity of 1 .mu.Ci/cm.sup.2 (37 Bq/g, or 1 nano Ci/g) for transport from the nuclear facility to a melting facility.
In this same area of using radioactive components in waste transport containers, U.S. Pat. Nos. 4,767,572 (Sappok) and 4,882,092 (Sappok), issued in 1989, teach use of radioactive residues in the formation of radiation shielding structures. They state that one would normally expect that the last thing which could be tolerated in a shielding material is a substance which itself is radioactive. In one embodiment, 25 weight % radioactive steel from reactor tubes, and the like, are reacted with 75 weight % of uncontaminated cast iron, and the mixture is melted to provide an alloy filler material. However, here, the amount of radioactive waste is tripled by reactive dilution with uncontaminated material. Other embodiments include use of broken up radioactive concrete as a shielding structure alone or in combination with comminuted, radioactive metal alloys. In all instances, however, to minimize detrimental contribution of radiation to the environment, the radioactive material must have a cobalt-60 equivalent between 1 to 100 Bq/g (0.027 to 2.7 nano Ci/g) before being used to make radiation shielding structures, or transport or storage containers. They state that this lower level is two orders of magnitude higher than natural activity levels which they identify as 0.01 Bq/g. It is also known to melt radioactive metal, such as scrap from nuclear power plants and the like, and recast it to form blocks that are used for shielding, such as is described in SEG Brochure "Metal Processing" Feb. 1991 No. 1165-291.
What is needed is an article which can effectively utilize high level radioactive waste as well as hazardous and mixed waste for a variety of useful purposes. What is also needed is a method of making a containment system where contaminated material, previously defined as radioactive waste, hazardous waste, or mixed waste can be used as part of the containment system itself, at high radioactivity levels and high hazardous waste levels, without expensive chemical decontamination steps, and without any substantial initial dilution by mixing or reaction with substantial amounts of uncontaminated materials, and where the radioactive, hazardous, or mixed elements in the waste can be fixed in the system, so that leaching is controlled and is not a problem. It is one of the objects of this invention to provide such an article, method, and containment system.
The present invention resides, generally, in the concept that contaminated material, of a wide variety, is suitable for use in making a wider variety of articles than heretofore has been recognized. The present invention also resides, generally, in the concept that it is possible to reduce to a more marked extent than previously recognized, the ratio of clean material used, to contaminated material, in making a large number and variety of articles, including but in no way limited to waste containers. The contaminated materials to which this invention is concerned are primarily radioactive, hazardous, or mixed waste.
Among the many uses for which this invention is applicable, the following are "articles", which serve to illustrate the scope of this invention:
Containers of every conceivable dimension, shape, weight, and capacity for processing temporarily or permanently holding, isolating, disposing, or preserving radioactive or hazardous materials, wastes, waste residues, spent materials, or by-products therefrom; which include radioactive waste or hazardous waste.
Shielding casks, pigs, bells, racks, grids, walls, panels, bricks, blocks, shot, sheet, wool, slabs, etc. that use contaminated lead, polyethylene or other plastics, water, depleted uranium, steels, and other metals, or other radioactive waste or hazardous waste.
Building structures including structural steel or members (beams, columns, posts), panels, t-sections, hollow core slabs, cinder blocks, bollards, curb stops, floors, floors, footer, skin, or modules thereof; which use contaminated concrete, steels, lead or other metals, or plastics or other radioactive waste or hazardous waste.
Linings, insulations, refractories, blankets, coatings that include contaminated materials including materials like contaminated steel fibers, shot, grit, dust and powders. Such linings etc. could be used on rail cars, truck bodies, caissons, open-top waste containers, impoundments, kilns, calciners, secondary combustion chambers, bulk storage facilities, silos, afterburners, quench towers, spray dryers, furnaces, ovens, and other similar thermal or chemical treatment equipment; which use radioactive waste or hazardous waste.
Impact limiters on corners, sides, or surrounding a waste container, made from contaminated polymers, plastics, rubber, organic composites (wood or cellulosic fibers), steel or metal shapes (tubes, grids, cages, etc.); which use at least one of radioactive waste and hazardous waste.
Rollers, breaks, spindles, shears, cutting and shaping tooling for contaminated materials; which use radioactive waste or hazardous waste.
Components for use inside normally contaminated environments including tools, dams, reactor fuel grids, tubes and tube sheets, nozzles, ducts, etc. in nuclear reactors, hot cells, glove boxes, fuel reprocessing facilities, nuclear weapon manufacturing and disassembly facilities, devices holding or containing radioactive sources, etc; which use at least one of radioactive and hazardous waste.
Seals, gaskets, o-rings and the like in applications exposed to radioactive or hazardous wastes and made from contaminated polymer, rubber, plastics, steels, metals, and the like; which use at least one of radioactive waste and hazardous waste.
Dunnage, shoring, bracing, and the like made from contaminated materials to secure radioactive or hazardous materials or wastes; which use at least one of radioactive and hazardous waste.
Water quality systems including settling tanks, ponds, clarifiers, flocculating tanks, sludge beds, grease and grit chambers and the like; which use at least one of radioactive and hazardous waste.
Molds for steel ingots, plastic components, concrete shapes, RIM containers, rubber containers, etc; which use at least one of radioactive and hazardous waste.
Road materials made with or consisting in part or in whole of contaminated materials such as rubber, concrete or stone, steel or other metals for subgrade, bitum course, precast slabs, level course bitum concrete filler and the like; which use at least one of radioactive and hazardous waste.
Conveyers, sluices, tunnels, pipes, galleys, weirs, box culverts, bridges, bridge decks and the like used to convey radioactive or hazardous materials; which use at least one of radioactive and hazardous waste.
Metal shapes of all kinds made for equipment supports, stands, piping, components, teeth, clogs, and other wearing components; which use contaminated steel or other metal.
Process vessels, glove boxes, conveyors, skid plates, rails, wheels, platforms, grids and catwalks; which use contaminated steel or other metal.
Steel wire for reinforcing, welded wire fabric, welded wire cages for holding filters in disposal containers, baghouse bags in place, bows for various tarp-like covers, reinforcing in rubber or polymer parts (conveyor belts, sheets, drop curtains); which use contaminated steel or other metal.
Steel and other metal fibers of all shapes, twists, bends, lengths, thicknesses and aspect ratios to reinforce, add bulk, densify, stiffen, strengthen, toughen or otherwise modify various polymer, rubber, concrete, and refractory materials; where the steel or other fibers are contaminated.
Filters and membranes, and other applications for containing or excluding radioactive or hazardous materials; which use sintered, contaminated steel or other metal.
Boots, gloves, bellows, sleeves, and flexible joints to isolate radioactive or hazardous materials from an environment, or to be used in such an environment such as a hot cell, reactor cavity, glove box, or air lock; which use contaminated polymers or plastics.
Targets for depleted uranium or other projectiles, articles being drop tested, items being crushed, obliterated, or made unrecognizable, such as for classified components, munitions, etc; which use contaminated steel, other metals, concrete or plastics.
Tanks, tank liners, bearings, skid or slip sheets, insulators, impact limiters, bumpers, and balls; which use contaminated polymers or plastics.
Spheres for limiting vaporization from chemical processing tanks; which use contaminated plastic.
Sheeting and bags, used extensively to control contamination in nuclear power facilities; which use contaminated thermoplastics.
Accordingly, in one of many embodiments, the invention relates to an article characterized in consisting essentially of: waste selected from the group consisting of a) radioactive waste, b) hazardous waste, and mixtures thereof. In one of many embodiments, the article can be a contaminated waste article, made solely from cast, cooled, melted, radioactive metal components, where the melted metal used in the article is preferably substantially free of slag residue and has a specific activity over 130 Bq/g, and where the article consists of unsupported cast metal.
We have found, surprisingly, that contaminated metal tubing from, for example nuclear power plants, when melted and separated from slag residue can be used without dilution or alloying with uncontaminated metals, to provide slabs and stand-alone containers for contaminated waste. Even if the contaminated metal has a specific activity level substantially above 100 Bq/g, such as, above 130 Bq/g, it is not detrimental and the metal is still useful. The ability to use materials with high specific activities, such as above 130 Bq/g, minimizes the need for uncontaminated filler or the like in the container or other article. Therefore, other embodiments of the invention are an article, comprising a member, the member consisting essentially of a material selected from the group consisting of a) radioactive waste, b) hazardous waste, and mixtures thereof in a matrix of either concrete binder or plastic resin binder. Also, an article, comprising a member, the member consisting essentially of a material selected from the group consisting of a) radioactive thermoplastic b) hazardous thermoplastic and mixtures thereof; or an article, comprising a member, the member consisting essentially of metal of which more than 35 weight % of the metal is radioactive. Thus, the article could be a member section component or other part structure.
We have discovered that hazardous waste and mixed waste can be used alone to make a wide variety of slab, brick, wall or other type articles. Another aspect of the invention resides in an article characterized as consisting essentially of: waste selected from the group consisting of a) radioactive waste, b) hazardous waste, and mixtures thereof, where, if radioactive waste is in metal form, such metal constitutes more than 35 weight % of the article. This article, during use, can and in most cases will be exposed to radioactive or hazardous waste and therefore become further contaminated. However the article, such as a container is not limited to being exposed to or containing waste. The article could be exposed to or contain various chemicals or other materials not considered contaminated or waste, or could be exposed to or contain "fresh" radioactive or hazardous materials. Use of more than 35 weight % metal will provide integrity for the structure and allow its use as a substantially self-supporting container or the like. Preferably when metal is used it will be substantially free of slag residue.
A preferred high density containment system with a variety of particulate size gradings has also been discovered, and the invention also resides in a containment system for radioactive, hazardous or mixed waste, characterized by having a structure containing a series of different sized particles to provide high interior void volume filling, where at least one fine particulate selected from the group consisting of silica fume and flyash particles and mixtures thereof is close packed between coarse particulate selected from the group consisting of filler, cement and aggregate particles and mixtures thereof, and also containing additives distributed therethrough, selected from the group consisting of uniformly dispersed bars, fibers, generally spherical particles and amorphous particles, and mixtures thereof, such that the containment system has a density over about 90% of theoretical density.
In the above embodiment, the particles and additives can be non-contaminated materials or contaminated materials. The containment system can be thin walled, that is, less than 5 cm thick. It can be a round, square, or other configured storage module, having a bottom, sidewalls and an associated attached lid. The containment system can have a closely attached plastic sheet about 0.2 cm to about 2.5 cm thick, covering at the inside of the system and/or the outside of the system. The contaminated material when used is distributed in the module walls and is not concentrated as a separate inner or outer layer or shield.
The article/structure containment system can be a thick or thin wall type structure of various configurations, for example, primarily plastic containers, radioactive containment shielding; a variety of other rigid or flexible structures, including enclosures, dividers, barriers, burial and storage modules, vaults, trench walls and bunkers.
We have also found very useful containment systems characterized by a structure containing a material selected from concrete or plastic resin, containing within its walls radioactive metal, in the form of discrete fibers constituting from 2 weight % to 55 weight % of the system having lengths from about 0.5 cm to about 20 cm where the system contains different sized particles to provide high interior void volume filling in the case of concrete, or resin impregnated porous metal mesh or discrete fibers in the case of plastic resin.
The invention further resides in a method of making a contaminated waste article characterized by the steps: (A) providing radioactive metal material selected from the group consisting of nickel, chromium, iron, steel, and mixtures and alloys thereof; (B) inspecting said radioactive material to segregate it according to metal type, to provide a metal feed; (C) transporting the radioactive metal feed to a melting furnace operating at a temperature over 1400.degree. C., to melt the radioactive metal feed and form a top impure radioactive slag phase if the feed is impure, and generally a lower level radioactive molten metal phase; (D) casting the radioactive molten metal phase into a radioactive article substantially free of the slag phase; and (E) cooling the cast article to provide a solid radioactive article. These articles could be bricks, wall structures, slabs, containers or the like. They could be transportable and placed in direct or indirect contact with contaminated material. Also the slag phase could be cast into a radioactive article.
The invention also resides in a method of mixing radioactive, hazardous, or mixed waste into a binder matrix to form a containment system for additional, highly concentrated radioactive or hazardous waste characterized by the steps of: (A) providing a contaminated material selected from at least one of: (i) radioactive material in small discrete form, (ii) hazardous waste material in small discrete form; and (iii) mixed waste in small discrete form; (B) mixing thoroughly: (i) about 100 parts by weight of a binder material and (ii) about 2 to about 570 parts by weight of the contaminated material to which no more than about 15 weight % of uncontaminated material has been mixed, to provide a homogeneous composition, in which the contaminated material is in discrete, non-agglomerated form throughout the binder; (C) forming the composition into a unitary, solid containment system which contains contaminated material, and binder acting as a matrix for the contaminated material; and (D) placing the containment system in direct or indirect contact with highly concentrated, radioactive, hazardous, or mixed waste.
The invention very specifically, also resides in a method of making a structure for radioactive, hazardous or mixed waste, utilizing radioactive, hazardous or mixed waste as a component of the structure, characterized by the steps: (A) providing quantities of radioactive material selected from the group consisting of radioactive metal, radioactive concrete, radioactive sand, radioactive gravel, radioactive plastic, radioactive liquid, and mixtures thereof; (B) processing the radioactive material without dilution with any more than about 15 weight % of nonradioactive material, to provide at least one of (i) bars, (ii) fibers, (iii) generally spherical particles, (iv) amorphous particles, (v) sheet plastic, and (vi) stabilized liquids; (C) mixing (i) 100 parts by weight of a binder material and (ii) 0 to about 25 parts by weight of hazardous waste material selected from the group consisting of hazardous solids, hazardous liquids and mixtures thereof, to which is then added (iii) about 2 to about 570 parts by weight of the processed, radioactive material, to provide a homogeneous composition; and (D) forming the composition into a unitary, solid structure. The term "amorphous" as used herein means not having a standard geometrical shape or having an irregular shape.
Most advantageously, the invention resides in a container characterized by having concrete and from 2 weight % to 55 weight % contaminated metal fibers having lengths from 0.5 cm to about 20 cm and a length:width aspect ratio of between 200:1 and 20:1 where the container contains different sized particles to provide high interior void volume filling and a high density, generally over about 90% of theoretical density. The term "high interior void volume filing" as used herein means most voids are filled, resulting in a low porosity low void structure.
The initial contaminated material provided can include, radioactive stainless steel tubes used in cooling nuclear reactors, which have been cut into small pieces, or melt cast into small fibers; radioactive concrete chunks and dust resulting from demolition of or around nuclear reactor structures; "plastic" or "plastic resin" which is meant herein to also include rubber sheets or gloves used to deal with hazardous materials, and other materials described later in the specification; ion exchange resins, beads, powders or slurries used in purification processes; powdered hazardous soil; polychlorinated biphenyls; and the like.
The contaminated materials are usually processed by one or more of cutting, grinding, shearing, heating, melting, melt-casting, pressing, and the like, to form small pieces or particulates less than about 50 mm diameter, or squares or fibers less than about 20 cm long. Preferably, only a small portion, of "uncontaminated material", herein defined as virgin, non-contaminated and non-radioactive material is mixed or reacted during processing, so that the volume of contaminated material is not substantially increased prior to mixing with binder. The binder material can be, for example metal, plastic, or a mixture of sand, aggregate and cement, with the possible addition of silica fume, flyash, and plasticizer.
It is essential to thoroughly mix and disperse the contaminated material into its binder, so that the binder forms a matrix containing and firmly binding the discrete pieces or particles of contaminated material. In most cases where the binder is concrete, the cement used will be clean and non-contaminated so that good bonding is achieved, the same is true if a thermoset resin, such as an epoxy resin, is used as the binder. Also, contaminated thermoset resin cannot be remelted and would not provide good bonding.
As distinguished from U.S. Pat. No. 5,402,455 (Angelo et al.), dealing primarily with fiber mesh reinforcement in a concrete container, this invention deals primarily with discrete particles of contaminated material in a wide variety of articles.
In order to uniformly disperse radioactive fibers and particles, when they are used, and prevent clumping/agglomeration and thus concentration of radioactive material, the fibers are preferably processed to within narrow length:width aspect ratios and the particles are preferably processed to within narrow particle sizes and gradation. In the case of concrete binder material, they are preferably combined with chemical plasticizer when incorporated into the binder material. Preferably, a series of different sized contaminated material and binder materials are provided, to allow a close, high density packing and elimination of most void volume in the cured system.
The term "radioactive" as used herein is defined to mean a level of activity, due to contamination or activation by, for example, radio-isotopes of cobalt, lead, cadmium, cesium, barium, or the like, ranging from 0.1 nano Ci/g to well over 10 nano Ci/g (3.7 Bq/g to well over 370 Bq/g). The contaminated materials used in substantially large volumes in this invention would otherwise have limited usefulness, and only be suitable for direct disposal in the absence of some dramatic technology that could remove the contamination. The containment system can contact or hold loose contaminated material directly, or contaminated material placed in standard or compressed steel drums, plastic containers, or the like, so that there is "indirect" contact of the containment system with the waste through contact with the steel drum or plastic container wall.
The processes of this invention as previously described provide an article, such as a containment system, which has low permeability to water, excellent leach resistance, and, additionally in the case of concrete, high tensile and compressive strength; and which can contain from 2 to 570 parts of radioactive or hazardous material per 100 parts of matrix material, providing a major means for disposal of radioactive or hazardous waste. In the case of a container for contaminated waste, this invention allows an increased payload of contaminated material in the walls of the container of from 10 weight % to 100 weight %, based on contained contaminated material filling the container, usually in the form of compressed drums of contaminated material. Thus, a substantial number of waste containers can be eliminated in transport and burial operations, representing tremendous savings, and minimizing transport operations.